Flexible rubber impeller pumps are generally used in the marine industry as raw water coolant pumps for diesel and gasoline internal combustion engines. The pumps draw water from a lake or ocean and either pump it directly to an engine, as is the case of pleasure boat engines, or through a heat exchanger as is the case of larger diesel engines. The rubber impeller in this variety of pumps typically includes an insert of a metal or plastic and a number of flexible blades. The rubber impeller needs to be periodically replaced due to wear and deterioration over time. Most manufacturers of flexible rubber impeller pumps recommend that the impeller be replaced at least annually. In addition, impeller failure can occur prematurely from various reasons, such as the pump suction being blocked or running in an adverse environment and such as in running water saturated with silt, sand, or other corrosive materials.
In the case of marine engines, when an engine overheats, one common check for maintenance personnel is to evaluate the impellers in the pump, which could be under less than ideal conditions. Conditions contributing to the deterioration of the impellers usually include usage in an overheating engine, cramped engine compartment, usage of inadequate tools for maintenance, and possibly a boat which may be adrift in rough seas and foul weather. The removal of the impeller for checking and possibly replacing is further complicated by the presence of corrosion and the build up of deposits between the impeller insert and the shaft.